1. Field of the Invention
The invention relates to molding compositions and engineering plastics having improved impact strengths, especially notched Izod strength. More specifically, the invention relates to blends of nylong and copolyesters which additionally contain polyesteramides, which have substantially improved impact strengths in combination with good flexural and tensile properties.
2. Discussion of the Background
Polymer blends or polyblends are mixtures of structurally different polymers or copolymers. Commercially important polyblends are generally mechanical polyblends which are made by melt-blending the various polymers in an extruder or other suitable intensive mixer. Polymer blending technology generally rests on the premise of property additivity, wherein the polymer blend has the combined properties which are found in each of the component polymers separately. A polymer blend can therefore have properties which are unavailable to the individual polymer components by themselves.
Blending of polymers is also cost efficient. Expensive polymers may be blended with inexpensive polymers to obtain a useful polyblend which has a cost:performance ratio that makes it very attractive for any given application. The standards of performance for any given application can therefore be met using blends of two known polymers without the need to develop completely new polymers and new plant equipment. There is a continuing need for novel and useful polymer blends.
Engineering plastics such as molding compositions should generally have a good balance of high tensile properties, stiffness, compressive and sheer strength as well as impact resistance and should be easily moldable. Their physical properties should be reproducible and predictable and they should retain their physical properties over a wide range of heat and chemical conditions. Engineering plastics should be able to resist mechanical stress for long periods of time.
Nylon polymers, and in particular nylon 6 and nylon 6,6, have been known since the 1950's and were one of the first engineering thermoplastics to become commercially available. Nylon may be injection molded or may be extruded into sheets, films or profiles as well as blow molded. The wide variability in the melt-processability of nylon engineering plastics has led to their extensive use in the formation of fibers and filaments, bottles, rods and tubes, as well as large injection molded and cast industrial, appliance and automotive parts. Polymer blends containing nylon are very important engineering plastics. The properties of the polymer blend containing nylon can be advantageously adjusted by blending nylon with other types of polymers to obtain a polymer blend having properties which cannot be obtained by either of the individual components of the polymer blend. There continues to be a need for new engineering polymer blends based on nylon to meet the increasing demands placed on engineering plastic components.